1. Field of the Invention
The subject power system is generally directed to an onboard power generation system for a host platform. More specifically, the power system is an onboard system wherein an advanced radioisotope heat source is employed in operating a generator module.
A number of different generator module types, including thermoelectric and thermodynamic generators, are known in the art. A type of generator module available for possible use in space vehicle applications is the Stirling engine/alternator. In this type of generator, a working fluid, such as helium, is contained within a sealed chamber. Sufficient heating of at least a portion of that chamber by an external heat source leads to alternating expansion and compression cycles of the working fluid by which the engine""s piston or other actuating member is reciprocally operated.
The technical advantages of a Stirling engine are well-known to those skilled in the art. Perhaps the most notable, at least in space vehicle applications, is its overall efficiency of operation. Compared to thermoelectric-type generators which exhibit an efficiency typically on the order of 7%, known Stirling engine-type generators typically exhibit a level of efficiency on the order of 25%. Consequently, Stirling engine-based generators require less fuel than thermoelectric generators to generate the same power output under comparable conditions. With nuclear systems in particular, a lesser fuel requirement translates rather directly to a lesser safety hazard, and thus yields generally a safer system.
Despite such operational advantages, actual implementation of Stirling engine-based generators in space applications presents substantial challenges not found with other generator types. One such challenge is to effectively achieve an intense transfer of heat from an external heat source to a precisely-defined and narrow annular region of the given Stirling engine generator(s). Unlike thermoelectric generator designs, for example, which afford a widely distributed planar area by which to provide the required heat transfer, Stirling engines require the heat transfer to occur at a highly concentrated heat exchanger header region defined thereon. The challenges are compounded not only by the extreme thermal and mechanical stresses encountered in space flight applications, but by the requirement to safely preserve containment of the heat source""s radioisotope fuel material, even when subjected to the environmental extremes encountered during reentry into the Earth""s atmosphere. There is, therefore, a need to provide a power system capable of accomplishing the dual function of adequately effecting the necessary transfer of heat to the given power generator and of preserving the given heat source intact during all phases of a given application to safely contain the radioisotope fuel material employed therein, even under the severest of possible conditions.
2. Description of the Related Art
Nuclear power systems are known in the art. Use of such systems to generate onboard power for a host platform are also known in the art, as are the use of those systems in space applications employing Stirling engine-type generators. Such known systems, however, do not adequately provide the combination of capabilities realized by the subject power system.
An approach known in the art is to utilize in a space application employing a Stirling engine generator a heat source designated by the U.S. Department of Energy as the General Purpose Heat Source (GPHS). The GPHS incorporates a rectangular block, or brick-like, fuel-containing structure. One or more GPHS blocks are placed in contact with the heat exchange region(s) of the given Stirling engine(s) to effect the necessary heat transfer. While the solid brick-configuration of the GPHS would enable it to survive reentry, it is far from ideal -at least in this contextxe2x80x94in effecting efficient heat transfer.
The GPHS brick configuration forms a solid outer structure that generates high drag when traveling through the atmosphere. This minimizes the structure""s velocity during reentry, consequently minimizing the structure""s heating during reentry and thereby heightening the likelihood that the structure would survive the reentry cycle. Notwithstanding this, the brick configuration makes for a cumbersome and awkward structure by which to transfer heat to a precisely limited heat exchange region upon a Stirling engine.
It is not an adequate solution to configure the GPHS with a central bore for receiving the heat exchange region of a Stirling engine therein. The resulting configuration would suffer enough compromise in structural strength, weight, and integrity that, absent other more significant additional modifications, the GPHS block in such configuration may very well be left without the ability to survive reentry. Its aerodynamic properties in this configuration may cause the GPHS block to fail, and thereby release its radioisotope fuel material into the atmosphere.
Hence, there remains a need to provide a power system that incorporates a radioisotope heat source capable of effecting highly efficient heat transfer to the given power generator subsystem, yet safely guards against unintended release of its radioisotope fuel material during all conceivable phases of system operation.
It is a primary object of the present invention, therefore, to provide a power system wherein highly efficient transfer of heat occurs between a radioisotope heat source and a power generator module.
It is another object of the present invention to provide a power system wherein the radioisotope fuel material remains securely contained, even when the system is subjected during use to extreme thermal and mechanical conditions.
It is yet another object of the present invention to provide a power system adapted for space applications.
It is still another object of the present invention to provide a power system wherein a radioisotope heat source capable of both effecting highly efficient heat transfer to a Stirling engine-based generator module and securely containing the radioisotope fuel material held therein even through reentry into the Earth""s atmosphere.
These and other objects are attained in the subject power system. The subject power system generally comprises: a generator module and a heat source substantially encircling at least a portion of the generator module in thermally conductive manner. The heat source contains a radioisotope fuel material. The generator module is formed with a heat exchanger section extending axially from a generator section. The heat source is defined by a plurality of separable arcuate aeroshell segments extending angularly about a portion of the generator module""s heat exchanger section to collectively encircle it, and to describe coaxially thereabout a substantially cylindrical outer contour. Each arcuate aeroshell segment has formed therein at least one fuel compartment extending axially inward from a front axial face. A covering member is coupled to the front axial face of an arcuate aeroshell segment so as to enclose its fuel compartment.
In one exemplary embodiment of the present invention, the power system comprises: an axially extended housing having a pair of opposed mounting members and an intermediate section extending axially therebetween so as to define an inner chamber. The system also comprises first and second heat engines disposed at least partially within the housing, as well as a substantially annular heat source disposed within the housing inner chamber. The mounting member includes a flange portion defined about a central opening and formed with a plurality of flexure openings that communicate with the inner chamber. Each heat engine includes a generator section and a heat exchanger section extending axially therefrom, wherein at least a portion of each generator section passes through the central opening of one mounting member, and the heat exchanger sections of the first and second heat engines are adjacently disposed. The heat source encircles a portion of each heat exchanger section of the first and second engines for thermally conductive coupling thereto. The heat source is defined by a plurality of separable arcuate segments extending angularly about their respective portions of the heat exchanger sections, with each arcuate segment storing therein a radioisotope fuel.